(Parts of this background may or may not constitute prior art.)
It has now been several decades since the start of the transition from copper wire telecommunications cable to optical fiber cable. In that transition the biggest change by far is the sensitivity of glass optical fibers to stresses in the cable. The electrical transmission properties of copper are relatively immune to mechanical forces. In contrast, the light transmission properties of optical fibers are significantly impacted by mechanical stresses on the optical fiber cable. There is a variety of these effects, and a variety of causes. This makes optical fiber cable design, while simple in concept, extremely complex in practice.
For many years Standard Multimode optical fiber (MMF) was manufactured with a core size of 62.5 and an overall dimension of 125 microns. Now, 50-Micron Multimode Fiber (50-MMF) is gaining popularity due to its expanded bandwidth and transmission distance potential over traditional multimode fiber runs. Providing nearly three times the bandwidth over twice the distance, 50-MMM fiber is recommended for new premise applications including intra-building connections.
However, compared to single mode fiber and 62.5MMF, 50-MMF tends to be far more sensitive to signal attenuation resulting from fiber microbending or macrobending caused by mechanical stress. As a result, recent studies show that some 50-MMF optical fiber cables can show significant signal attenuation in standardized mechanical qualification tests, while older SMF cables show minimal signal attenuation in those tests.
This problem is exacerbated by end-user demand for smaller optical fiber cables with increased fiber packing density. Traditionally, indoor distribution cables with 50-MMF employ tight buffer coatings over each individual fiber, to provide mechanical protection to the individual fibers. Common tight buffer diameters include 900 micron and 600 micron. Distribution or trunk cables employing tight-buffered fibers tend to be large and bulky, providing challenges to the end-user. First, it is often difficult for end-users to route these large cables directly to connection or interconnection points on equipment, or within shelves or trays. End-users must often transition from the large buffered fiber distribution cable to smaller, flexible interconnect cables. However, this adds cost and complexity to installations. Second, in large data centers or storage-area networks, a large number of distribution cables are often needed for interconnection of equipment. Use of large distribution cables can fill up limited space in overhead or underfloor cable trays, as well as restricting flow of cooling air. There is end-user demand for compact, high-density distribution cables with 50-MMF which can be directly routed to interconnection points.